the difference is seaier to detect. I usually do a walk through when checking out a room where speakers were installed, one reversed speaker connection can be percieved as a hole in the sound. if you stand half way between speakers and listen with one speaker reversed and not reversed yhou can hear the difference. however it makes no difference to the amplifier if the signal is invefrted or not, only the ears perception of where the sound comes from.

 

Certainly the ear can detect a relative phase differences between two speakers or likely relative phase differences between fundamental and harmonics, but there is no reference for the ear to hear an absolute phase difference if the total signal is simply inverted. To be detected a phase difference has to be relative to something and to detect that the ear (or measuring instrument) must have simultaneous access to both the original signal and the phase-shifted signal.

 

Certainly the ear can detect a relative phase differences between two speakers or likely relative phase differences between fundamental and harmonics, but there is no reference for the ear to hear an absolute phase difference if the total signal is simply inverted. To be detected a phase difference has to be relative to something and to detect that the ear (or measuring instrument) must have simultaneous access to both the original signal and the phase-shifted signal.

I think the point is that what you say is true for a signal that has symmetrical + and - half cycles. But for music signals this is not always the case.

Now if, as has been suggested, the ear is only sensitive to half the signal


Perhaps some one would like to try this with a diode and report?

Then it depends which half for an asymmetrical waveform.

Further for an asymmetrical waveform if the positive half waves are meant to produce compressions and the negative half wave therfore produces rarefactions is the ear sensitive to this, again as it has been suggested?

 

#1: I know in audio signal processing it is important to preserve a constant phase and group delay through the passband. From this, I suppose the best approximations are:

• Bessel
• Butterworth
• Inverse Chebyshev

Am I right ? What are your suggestions about the topic ?

Depends on your intent.

The most common frequency-shaping filter is probably the Butterworth because of its flat passband.

Chebyshev is avoided in audio when the fidelity of the passband is important, which is usually.

Bessel is usually avoided as a frequency-shaping filter because the corner is too gradual. I heard or read somewhere that it's often used as a post-DAC filter due to its phase characteristics, with an additional circuit (or modification) to sharpen the corner. I can't remember where I heard this, so take it with a grain of salt.

 

The Bessel function has constant group delay, which is very good for audio. Also, it has the same attenuation slope as most other filters, 6 dB per octave per pole. But the Bessel filter gets there more graeually, with a rounder corner between the pass band and the stop band. That round corner is why it has such good phase response.

ak